The present invention relates to a method and apparatus for data access over a wireless link, in which a greater data rate may be provided in one direction of a link than in an opposite direction of the link.
In a fixed wireless access (FWA) telecommunications system, subscribers are connected to a backbone telecommunications network by means of radio links in place of traditional copper wires. Each of a plurality of subscribers is provided with a subscriber radio terminal at their subscriber premises. A base station provides cellular coverage, typically in urban environments over a 5 km radius, with the plurality of subscriber radio terminals. Each base station may be connected to a backbone network, eg a Public Switched Telecommunications Network (PSTN) switch via a conventional transmission link, known as a backhaul link thereby providing the plurality of subscribers with access to the PSTN. A single base station can serve of the order of up to two thousand subscribers, making the installation and maintenance cost of a fixed wireless access system lower than that of an equivalent copper wire access network.
Referring to FIG. 1 herein, there is illustrated schematically a radio base station and subscriber terminal of a prior art fixed wireless access system. A plurality of subscriber radio terminals 100 each comprising a transceiver 101 and an antenna 102 communicate with a radio base station 103 having a base station antenna 104 and a base station transceiver apparatus 105. A plurality of such radio base stations 103 each communicate with a central office switch 106 to gain access to a backbone telecommunications network, eg a Public Switched Telephone Network (PSTN). In a geographical area, a plurality of base stations are distributed to provide coverage in a cellular pattern. Each base station 103 is connected to a local exchange switch 106 via a backhaul transmission line 107 which may comprise for example a terrestrial line eg fiber optic cable or coaxial cable, or a microwave transmission link. Communication between the subscriber radio terminal and the base station is via a wireless radio link 108. Each local wireless link 108 between radio base station 103 and subscriber radio terminal 100 comprises an uplink from the subscriber antenna to the radio base station antenna, and a downlink transmitting from the radio base station antenna to the subscriber antenna and transceiver. Each radio base station operates either an omni-directional beam or a plurality of broad sectorized beams encompassing all subscribers in a cell or sector for receive and transmit, whereas each subscriber radio terminal operates a directional pencil beam directed at the base station for receive and transmit. In a prior art fixed wireless access deployment, although each nominally hexagonal cell is served by a base station located nominally at the center of the cell, current technologies permit the base station antenna to be located non-centrally within a cell area.
In the prior art fixed wireless access system a frequency spectrum allocation for the uplink is typically of a same bandwidth as a frequency spectrum allocation for the downlink. For example, the uplink may be allocated 15-17 MHz bandwidth in an available radio spectrum, and the downlink may be allocated a further 15-17 MHz bandwidth of frequency spectrum. The uplink and downlink spectrums are spaced apart by typically around 50 MHz, referred to as duplex spacing.
Typically, the uplink frequency allocation of 15 MHz is subdivided into a plurality of 300 KHz slots each occupied by a separate carrier frequency, giving 48 uplink carriers. For a 17 MHz uplink band, divided into a plurality of 300 KHz uplink frequency slots, 54 uplink carriers are available. Similarly, the allocated downlink frequency spectrum is subdivided into a plurality of 300 KHz downlink frequency slots, being symmetric with the uplink frequency allocation.
The 300 KHz frequency slots are allocated to a plurality of radio base stations over a geographical area according to a repeating frequency reuse pattern. To minimize the likelihood of interference, adjacent cells within a fixed wireless access network, or sectors within each such cell are allocated distinct groups of radio frequencies selected so as to minimize the likelihood of a transmission with any cell (or sector of a cell) causing interference in any other cells or sectors nearby. On the uplink, in a three of nine reuse pattern, every ninth frequency is reused, so although only 18 of the 54 available carrier frequencies are used per cell, the frequency pattern can be reused indefinitely, and an allocation of subscriber radio terminals to base stations giving service to around 2000 subscribers per cell can be replicated indefinitely over a geographical area.
Thus, typically in a 17 MHz uplink case, each base station may operate 18 carriers, 6 per sector, in a tri-sectored arrangement. Each carrier frequency is separated into 10 bearer time slots, providing 60 uplink bearer time slots per sector (180 bearers per cell). Of these, 2 to 6 bearer time slots per sector are reserved for an access channel, through which subscriber radio terminals request access to the radio base station leaving 54 bearer time slots per sector available for subscriber usage. Each subscriber radio terminal operates two subscriber lines, so taking account of the bearers reserved for access channels, up to a maximum of 27 radio subscriber terminals in a sector can communicate with a base station at the same time. However, as usage of subscriber terminals is statistical in nature, up to approximately 600 to 700 subscribers per sector can be accommodated since not all subscribers communicate at once.
Similarly, in the 17 MHz downlink band, the downlink frequency allocation at each base station is 18 carriers per cell, each downlink carrier corresponding to an uplink carrier in a frequency division duplex pair. In each sector, there are 6 downlink carrier frequencies, corresponding with the 6 uplink frequencies, to form 6 frequency division duplex pairs per sector. As with the uplink carrier frequencies, the downlink carrier frequencies are time division multiplexed into a plurality of bearer timeslots. Some of those bearer timeslots are used as a downlink broadcast channel which advertises available bearer timeslots to all subscribers within a sector.
For circuit switched services carried over the wireless link, where those services are characterized by having symmetric constant data rate traffic both on the uplink and downlink, eg voice traffic, the prior art symmetric allocation of frequency spectrum between the uplink and downlink beams is relatively efficient. However, for services which entail an asymmetric data rate requirement as between the uplink and the downlink, for example where the volume of traffic data on the uplink differs greatly from a volume of traffic data on the downlink, a symmetric frequency spectrum allocation for the uplink and downlink beams is inefficient. For example, taking an instance of a subscriber making Internet communications on a user terminal 109, connected to a subscriber radio terminal 100, a request for data sent to an Internet service provider 110 on the uplink may comprise a transmission of packets of tens or hundreds of Bytes. On the other hand, service data provided by the Internet service provider may comprise data units of the order kBytes or MBytes. Such data is downloaded from the local exchange 106 over the backhaul system 107 through the base station 103 and over the downlink. In a circuit switched application, the bandwidth is reserved and available for use for uplink and downlink communications throughout the duration of a communications session. During the download of data from the Internet, the uplink path remains reserved for use by the subscriber, although no data traffic may be actually flowing on that uplink.
In a fixed wireless access network deployment having a plurality of subscribers each communicating with a base station, under conditions of services of asymmetric data rate, having a symmetric frequency spectrum allocation for a downlink and uplink path for each subscriber represents an inefficient use of frequency spectrum.
However, in many applications, a symmetric frequency allocation is all that is available, due to prior allocation of frequencies by license. Frequencies may become available due to de-commissioning of legacy equipment using symmetric uplink and downlink frequencies and any replacement equipment must make use of the symmetric frequencies allocations becoming available.
In addition to the wasteful allocation of spectrum on the uplink, while data is being transmitted only on the downlink in the conventional circuit switched FWA system, there is also an additional inefficiency due to a time overhead associated with connection setup and tear-down, which adds further to the overall inefficiency of symmetric circuit switched fixed wireless access networks when carrying data traffic having an asymmetric downlink/uplink data flow.
One object of the invention is to provide an improved apparatus and method for fixed wireless access network operating a symmetric uplink and downlink frequency spectrum allocation, enabling such a network to transport services characterized by having an asymmetric data rate as between uplinks and downlinks, more efficiently over the symmetrically allocated uplink/downlink frequency spectrums.
According to a first aspect of the present invention there is provided in a cellular communications system comprising a plurality of base stations, each communicating with a plurality of subscriber radio terminals, a method of communicating between a radio base station and a said plurality of subscriber radio terminals, said method comprising the steps of:
at said base station:
receiving packet switched data carried on an uplink frequency of a frequency division duplex pair; and
transmitting packet switched data on a downlink distribution channel carried on an unpaired downlink frequency.
Preferably said uplink packet switched data is carried on a contention access channel.
Said contention access channel may comprise a slotted ALOHA channel.
Preferably said uplink packet switched data shares said contention access channel with a plurality of connection requests for circuit switched traffic.
Said uplink packet switched data may comprise a request for services having an asymmetric data rate as between a source and a destination of said service.
According to a second aspect of the present invention there is provided a method of communicating between a radio base station and a plurality of subscriber radio terminals, said method comprising the steps of:
receiving a plurality of service requests from said plurality of subscriber radio terminals at said radio base station;
recognizing said service requests received at said radio base station;
in response to a said service request, forwarding said service requests to a service provider apparatus;
receiving service data in response to said service request signal; and
transmitting said service data to said plurality of said subscriber radio terminals.
Preferably said step of receiving a said service request comprises receiving said service request over a directional uplink transmission beam.
Preferably said step of transmitting said service data comprises transmitting said service data on a sectorized downlink beam.
Preferably said service requests are received on an uplink access channel and said service data is transmitted on an unpaired downlink frequency.
Preferably said downlink distribution channel carries data traffic in response to one or a plurality of service requests received on an uplink access channel.
According to a third aspect of the present invention there is provided a method of allocating frequency spectrum slots at a radio base station, said radio base station configured for communicating with a plurality of subscriber radio terminals, said method comprising the steps of:
allocating a plurality of frequency division duplex pairs for communication between said subscriber radio terminal and said plurality of radio base stations, each said frequency division duplex pair comprising an uplink frequency and a downlink frequency; and
allocating an unpaired frequency for communicating on a downlink from said base station to said plurality of subscriber radio terminals.
Preferably said unpaired downlink frequency is operated to carry packet switched data.
Preferably said radio base station operates a plurality of sectorized beams, and a said unpaired downlink frequency is operated for each said sectorized beam.
The invention includes a radio base station configured for operating the method as described in the third aspect.
According to a fourth aspect of the present invention there is provided a method of allocating bearer channels at a radio base station, configured for communicating with a plurality of subscriber radio terminals, said method comprising the steps of:
allocating a plurality of paired bearer channels for carrying circuit switched data, each said bearer channel pair comprising an uplink channel carried on an uplink frequency slot, and a downlink bearer channel carried on a downlink frequency slot; and
allocating packet switched data to a plurality of unpaired downlink bearer channels.
Preferably said unpaired bearer channels are carried on an unpaired downlink frequency, and said paired bearer channels are carried on one or a plurality of frequency division duplex pairs.
According to a fifth aspect of the present invention there is provided a radio base station comprising:
a first antenna and transceiver apparatus configured to operate a plurality of frequency division duplex pairs, each said frequency division duplex pair comprising an uplink frequency and a downlink frequency;
a second antenna and a transmitter apparatus configured for transmitting at least one unpaired downlink frequency.
Said first antenna and transceiver apparatus may comprise means for distinguishing between service request signals for packet switched data services and connection request signals for circuit switched services received on said uplink frequencies of said frequency division duplex pairs; and
means for routing service data received in response to said service requests, to said second antenna and transmitter for broadcast of said service data by said second antenna and transmitter.
Preferably the base station operates to transmit packet switched data on said second antenna and transmitter.
Said subscriber radio terminal may further comprise:
an antenna for receiving and transmitting over a frequency division duplex pair comprising an uplink frequency and a downlink frequency;
a transceiver apparatus configured for transmitting on said uplink frequency and receiving on said downlink frequency of said frequency division duplex pairs; and
a receiver configured for receiving signals on an unpaired downlink frequency.
Said subscriber radio terminal may further comprise a multiplexer, wherein said receiver operates to receive signals from said antenna via said multiplexer, said multiplexer operating to multiplex between signals assigned to said transceiver and signals assigned to said receiver.
Said subscriber radio terminal may comprise a further antenna adapted for receiving said signals on said unpaired downlink frequency, wherein said receiver operates to receive signals from said further antenna.
The invention includes an asymmetric data access scheme, wherein short message uplink traffic is carried on a shared access uplink channel.
The uplink channel may carry Internet data requests.
The invention includes a fixed wireless access base station operable to provide asymmetric data access and operable to receive and route uplink traffic received via a shared access channel. The uplink channel may comprise Internet data requests.
The invention includes a fixed wireless access subscriber apparatus operable to provide asymmetric data access and operable to receive and route uplink traffic received via a shared access channel.
The fixed wireless access system may comprise a proxy server. The system may comprise a fixed wireless access base station wherein the proxy server is located at said base station.
The invention includes a radio transmission system comprising a local subscriber interface and a radio interface and adapted to communicate with a remote base station by means of an access channel, wherein an Internet request is emitted from the radio interface, encoded on the access channel responsive to receipt of the Internet request on the local subscriber interface.
The invention includes a satellite base station operable to provide asymmetric data access and operable to receive and route uplink traffic received via a shared access channel. The uplink traffic may comprise Internet data request.
The invention includes a satellite subscriber apparatus operable to provide asymmetric data access and operable to receive and route uplink traffic received via a shared access channel.
Said uplink traffic may comprise Internet data requests.
The invention includes a satellite system comprising a proxy server. The system may comprise a base station wherein said proxy server is located within said satellite.